Caption: Diagram illustrating divergent plate boundaries creating larger ocean divide (at middle), and convergent plate boundaries resulting in volcanic lands (at right). The mid-ocean ridges (at middle) are one of the three basic types of plate boundaries. As shown here they are divergent and are spreading. They spread from forces, produced by mantle convection and gravity, that pull the oceanic lithosphere in opposite directions (shown by dark blue arrows). As the plates are pulled apart, magma is extruded from the mantle to fill in the void. At right, plates are converging; crust is destroyed and recycled back into the interior of the Earth creating a volcanic arc as one plate dives under another.